Heat exchangers for blood are used extensively in sophisticated medical processes. When cardiovascular surgery is performed, for example, a "heart-lung" machine is employed to pump and oxygenate a patient's blood while the patient's heart is stopped. Often, the patient's body temperature is artifically lowered to reduce the patient's physiological processes to thereby reduce the patient's need for oxygenated blood. During coronary revascularization, profound hypothermia in conjunction with topical cooling protects the myocardium during ischemic periods at the time of surgery. A typical heart-lung machine may include, in series, a reservoir to collect blood from the patient, a pump to maintain blood flow, a heat exchanger to warm or cool the blood and an oxygenator, blood returning to the patient from the oxygenator. Other elements, of course, may be included within the extra corporeal circuit such as means for removing bubbles from the blood and the like.
It will be understood that a considerable volume of blood or other fluid is required to "prime" or to fill a heart-lung machine so that the same may be operated. In practice, the machine may be primed with non-cellular fluids with or without the addition of blood from a blood bank or previously taken from the patient.
The heat exchanger in the apparatus described above may be employed to reduce the blood temperature of a patient before heart surgery begins, and subsequently may be used to reheat the blood to a normal body temperature at the conclusion of the operation. Reusable tube-and-shell heat exchangers of stainless steel are widely used for this purpose. The conditions which are imposed upon such reusable heat exchangers, however, render heat exchangers of this type extremely expensive and costly. The cleaning effort after each use in arduous. With one commerical heat exchanger of this type, for example, the heat exchanger must be completely disassembled after each use, thoroughly cleaned, and then reassembled--a task which requires a number of hours. The reassembled heat exchanger must, of course, be sterilized, and great care and skill is required in the cleaning operation.
Generally, a heat exchanger of the type described must be capable of rapid heat exchange over rather narrow temperature differentials, and yet must avoid turbulence or other disturbances with blood which might lead to blood damage. Thus, large pressure drops and turbuence in the flow of blood through the heat exchanger--which ordinarily would be desired to increase the rate of heat transfer--must be avoided. Further, the heat exchanger should require the smallest possible amount of blood or other liquid for "priming".
It would be highly desirable to provide an inexpensive, easily manufactured, disposable blood heat exchanger which would provide good heat exchange over narrow temperature differentials, which would operate with a low pressure differential thereacross, and which would maintain the blood in gentle laminar flow through the exchanger.